Hello: The problem with heating any fuel fired tank that isn’t full of water is that the uncovered part of the flue must get quite hot as water can’t keep it cool. From there you get thermal expansion of the steel flue, creating stresses in the tank. You might also damage the lining, particularly if water does touch the hot surfaces.
Letting the Mag Erad work longer could help. Adding a little preheated water could help. I’ve never seen any disasters using this product, but then I avoid disasters in my work 😎
I no longer make the Muck Vac, but anyone with a mechanical bent is welcome to give it a try.